TPE Injection Moulding: Practical Thermoplastic Elastomer Guide
Thermoplastic elastomer (TPE) is not one resin. It is a group of rubber-like thermoplastics used when a part needs grip, compression, repeated flexing, or a soft over-moulded surface without vulcanised rubber tooling. Nordmould can support TPE as a standalone moulding material and as the soft shot in insert or two-component over-moulding, with production starting from 100 pieces.
The grade matters more than the label. A Shore 40A SEBS grip, a TPV automotive gasket, and a TPE-E connector boot all process as TPE, but they do not behave the same in heat, oil, compression, or ejection.
What are the mechanical and thermal properties of TPE?
TPE covers several chemistries. The most common injection-moulding families are styrenic block copolymers (SBS and SEBS), thermoplastic vulcanisates (TPV), and thermoplastic polyester elastomers (TPE-E / COPE). Values below are representative ranges only; production selection should always use the resin supplier's datasheet for the exact grade and hardness.
| Property | SEBS (Shore 40A) | SEBS (Shore 60A) | TPV (Shore 55A) | TPE-E (Shore 40D) |
|---|---|---|---|---|
| Tensile strength | 3-10 MPa | 6-15 MPa | 5-12 MPa | 20-35 MPa |
| Elongation at break | 400-800 % | 300-750 % | 300-600 % | 200-450 % |
| Compression set (22-24 h / 70 °C) | 35-80 % | 20-45 % | 15-30 % | 20-45 % |
| Continuous service temp | -40 to 90 °C | -40 to 100 °C | -40 to 120 °C | -40 to 130 °C |
| Water absorption (24 h) | < 0.1 % | < 0.1 % | < 0.1 % | 0.2-0.5 % |
| Density | 0.88-1.00 g/cm³ | 0.90-1.02 g/cm³ | 0.95-1.05 g/cm³ | 1.15-1.25 g/cm³ |
| Shrinkage | 0.5-2.5 % | 0.5-2.5 % | 0.8-2.0 % | 0.8-1.8 % |
Compression set is the number buyers should watch on seals and gaskets. A soft SEBS can feel good in the hand but recover poorly after long compression at elevated temperature. TPV is usually the safer TPE family for hot static seals; TPE-E is used when the part needs more strength and chemical resistance than a soft-touch grade can provide.
What are the typical applications of TPE injection moulding?
TPE is used when a hard plastic part needs a controlled soft zone, or when the complete part has to flex and recover.
Soft-touch over-moulding: Power tool handles, toothbrush handles, kitchen utensil grips, and handheld electronics controls often use TPE over a rigid ABS, PP, PC, or nylon substrate. The rigid part carries the load; the TPE provides grip, sealing, or vibration damping. Insert moulding can work for lower volumes, while two-shot tooling is usually cleaner for repeat production.
Seals and gaskets: Softer TPE grades, often Shore 20A-40A, are used for dust seals, static gaskets, caps, cable glands, and consumer electronics membranes. TPV is preferred over SEBS when the seal sees heat, weather, or sustained compression.
Medical and personal care: Selected TPE grades are available with ISO 10993 test packages or food-contact declarations. They are used for mask seals, syringe plunger components, soft-tip instruments, and baby-care products. Compliance is grade-specific; the material certificate and intended body contact must be checked before quoting a regulated part.
Footwear and apparel hardware: Shoe components, buckles, clips, and flexible trim use TPE where colour, soft touch, and moderate wear resistance matter more than high tensile strength.
Automotive: Interior soft-touch trim, small seals, grommets, and vibration-damping parts often use TPV or higher-temperature TPE grades. Under-bonnet parts need a grade with proven heat ageing and fluid resistance, not a generic soft-touch compound.
How is TPE processed in injection moulding?
Most TPE grades run on standard injection-moulding machines. The tooling and process still need to be designed around soft ejection, higher shrinkage than many rigid plastics, and the bond line if the part is over-moulded.
| Processing parameter | SEBS / SBS | TPV | TPE-E |
|---|---|---|---|
| Melt temperature | 170-220 °C | 190-230 °C | 220-260 °C |
| Mould temperature | 20-40 °C | 20-50 °C | 20-70 °C |
| Injection pressure | 35-100 MPa | 50-100 MPa | 50-120 MPa |
| Shrinkage | 0.5-2.5 % | 0.8-2.0 % | 0.8-1.8 % |
| Recommended draft angle | ≥ 2° per side | ≥ 2° per side | ≥ 1° per side |
Gate design for over-moulding: the gate must let the TPE wet the substrate evenly without trapping air along the interface. Fan gates or multiple small gates often behave better than a single centre gate on broad soft-touch pads. Gate position should be reviewed before tool design because it affects weld lines, peel direction, and the visible vestige.
Ejection: soft TPE parts need more draft than rigid plastics. Use 2° as a practical minimum and 3° or more for very soft or textured surfaces. Large ejection areas, stripper plates, sleeve ejectors, and polished shut-offs reduce stretching and tearing compared with a few small ejector pins.
Bonding in over-moulding: chemical adhesion is grade- and substrate-dependent. Mechanical interlocks, through-holes, wrap-around edges, or undercut windows give the soft shot something to hold when peel loads are expected. Nordmould can review these features during DFM, but the final bond should be validated on the chosen resin pair.
What grades and variants of TPE are available?
| Family | Key feature | Typical use case |
|---|---|---|
| SBS (styrenic) | Low cost, good clarity | Toys, disposable grips, low-duty soft parts |
| SEBS (styrenic, saturated) | Better UV and heat stability than SBS | Outdoor grips, PP and ABS over-moulds |
| TPV (thermoplastic vulcanisate) | Lower compression set, better heat ageing | Seals, gaskets, automotive trim |
| TPE-E / COPE | Higher strength and oil resistance | Flexible connectors, boots, semi-structural parts |
| TPE-A (PEBA) | Broad temperature range and low-temperature flexibility | Sports equipment, footwear, cable components |
| Medical-grade SEBS | Biocompatibility test packages available | Mask seals, medical grips, baby-care parts |
Nordmould can quote common SEBS and TPV grades as primary TPE options. TPE-E, TPE-A, food-contact, and medical-oriented grades should be confirmed at RFQ stage because certification scope, colour, and supply lead time vary by compounder.
What are the advantages and limitations of TPE?
Advantages:
- Rubber-like flexibility and soft touch without vulcanisation
- Clean in-process regrind can often be reused in the same grade
- Broad hardness range, from very soft Shore A compounds to semi-rigid Shore D grades
- Grade families exist for PP, ABS, PC, PA, and other over-moulding substrates
- Food-contact, low-odour, medical-oriented, and bio-based options are available in specific grades
- Standard thermoplastic processing keeps tooling and cycle development closer to rigid plastic moulding than to rubber moulding
Limitations:
- Compression set is worse than vulcanised rubber in demanding sealing applications
- Soft grades can drag, tear, or deform during ejection without generous draft and support
- Oil, fuel, solvent, and disinfectant resistance varies sharply by TPE family
- Tensile strength is much lower than rigid engineering plastics and many TPU grades
- Creep under sustained load is significant in softer grades
- The wrong TPE family can pass a first-article check and still fail later in heat, UV, oil, or compression
When should you choose TPE over alternative materials?
Choose TPE over silicone when the part needs thermoplastic over-moulding, clean regrind, colour matching, or a lower-cost route for non-high-temperature service. Silicone is stronger above roughly 120 °C and remains the better choice for many implant, high-temperature, and long-compression seal applications.
Choose SEBS over SBS for outdoor exposure, UV exposure, or service above about 70 °C. SBS is cheaper, but SEBS resists heat and weathering better.
Choose TPV over SEBS for gaskets and seals where low compression set is required, especially above room temperature. SEBS can work for soft feel and light sealing, but TPV is usually more robust under hot sustained compression.
Choose TPE over TPU when soft touch, easy flow, lower processing sensitivity, and cost matter more than abrasion resistance. Use TPU for wheels, scraper lips, oily seals, cable strain reliefs, and structural flexible parts that need higher tensile strength.
Recyclability and sustainability
TPE is thermoplastic, so it can be remelted. In-process regrind from sprues, runners, and start-up scrap is often usable at controlled levels, commonly around 10-20 %, when it is clean, dry, and the same grade. Critical sealing, medical, food-contact, and colour-controlled parts may exclude regrind or require a lower percentage.
Post-consumer TPE recycling is harder. Parts are often small, bonded to another polymer, coloured black, or unidentified in the waste stream. For sustainability-driven projects, ask early about mono-material design, compatible over-moulding pairs, ISCC/mass-balance options, recycled-content grades, or bio-based TPE compounds.
Contact Nordmould with the STEP file, target hardness, service temperature, and any oil, skin, food, or medical-contact requirements. A free DFM review can cover grade family, over-moulding bond strategy, draft, ejection, and an indicative quotation path.
Frequently asked questions
What Shore hardness range is available for TPE injection moulding?
Injection-moulding TPE grades commonly run from about Shore 20A to Shore 70D, depending on the chemistry. Soft-touch over-moulds are often Shore 40A-60A. Structural-flexible parts use harder grades, often in the Shore D range. Nordmould can help narrow the hardness during DFM, but the final value should be tied to a resin datasheet.
Can TPE be over-moulded onto rigid plastic substrates?
Yes. TPE over rigid ABS, PP, PC, or nylon is a common two-shot or insert-moulding route. The grade and substrate must be matched: some styrenic TPEs bond well to PP and ABS, while other combinations need mechanical interlocks or adhesion-promoted grades. Bond strategy should be confirmed during DFM and quoting.
Does TPE require drying before injection moulding?
It depends on the TPE family. SEBS and SBS grades often have low moisture sensitivity and may not need pre-drying if stored correctly. Polyester-based TPE-E/COPE and some specialty grades should be dried to the resin supplier's datasheet, commonly around 80-110 °C for 2-4 hours.
What is the difference between TPE and TPU for injection moulding?
TPE is a broad family of rubber-like thermoplastics. TPU is one thermoplastic elastomer chemistry, but it is usually treated separately because it has higher tensile strength, better abrasion resistance, and better oil resistance than most soft-touch TPE grades. TPE is usually chosen for hand feel, easier processing, and cost control.
Can TPE parts be recycled?
TPE is thermoplastic, so clean sprues, runners, and rejects can often be reground and blended back into the same grade. End-of-life recycling is possible in principle, but it depends on the formulation, colour, contamination level, and whether a recycler can identify and sort the material.
What wall thickness is recommended for TPE injection-moulded parts?
A TPE wall thickness of 1.5-5.0 mm is a practical starting range. Softer grades can fill thin details, but ejection and tear risk increase. Sections above about 6 mm cool slowly and can show voids or sink, especially where wall thickness changes abruptly.
What does TPE injection moulding cost at Nordmould?
TPE tooling at Nordmould starts from €3,000, and production runs start from 100 pieces. Softer specialty grades and over-moulded parts cost more than simple single-shot commodity plastics. Exact pricing is provided after DFM review and written quotation.
What surface finishes work well on TPE parts?
Matt and fine textured finishes work well because they hide handling marks and support the soft-touch feel. Gloss is possible on harder TPE grades, but soft grades tend to show drag, gloss variation, and contact marks. Texture depth must be matched with enough draft for clean ejection.